Macrocomposite guideway and rail produced therefrom

ABSTRACT

A method of producing a macrocomposite linear guideway, wherein the “traditional” or existing rail material (e.g., hardened steel) is maintained as the wear resistant, low friction material in a layer having a surface intended to be in physical contact with one or more bearings, and further wherein this layer is supported by a substrate comprising a stiff, lightweight material. The wear resistant layer is attached to the substrate by a coating process. A linear guideway is also provided having a rail made of a lightweight stiff material on which is a hard bearing layer formed by a coating process.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application Number 60/339,788 filed Oct. 26, 2001, which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The instant invention relates to linear guideways for low friction, linear motion of one structure of a machine with respect to another. More specifically, the invention relates to a linear guideway having a rail portion for use in high acceleration applications such as in semiconductor fabrication.

[0004] 2. Description of the Related Art

[0005] Bearings are used in machines to provide low friction, uniform motion of one or more components relative to one or more other components. Bearings can be categorized as “contact” or “non-contact”. The latter category includes the gas bearings and those bearings that rely upon the maintenance of a hydrodynamic film for their operation. Contact bearings, on the other hand, feature an actual physical contact between the components that move with respect to one another. Slide bearings specifically provide for low friction linear motion, and are sometimes referred to as “linear bearings”.

[0006] Linear guideways come in a number of varieties. Some forms have ball bearings or roller bearings sandwiched between two (or more) longitudinal rails having hard, flat surfaces. The rail surfaces often function as housings or tracks for the bearings, with one of the rails attached to, for example, the base of the machine, and the other rail attached to the table, stage or surface that is to be in motion relative to the base. The rails are typically made from tool steel.

[0007] Typically, a plurality of linear guideways is required in each machine, as motion usually must be controlled in more than one dimension or degree of freedom. In addition, machines often require more than one linear guideway per travel dimension.

[0008] In certain applications, such as semiconductor wirebonding, the faster the workpiece can be moved, the more productive is the machine. Moving the workpiece about implies that it is to accelerated/decelerated, and the magnitude of such accelerations is governed by the equation F=m a, “force equals mass times acceleration.” The applied force correlates with the power of the motor driving the movable stage on which the workpiece is mounted. For a driving motor of given power, the speed to which the workpiece can be accelerated is inversely proportional to the mass to be accelerated. Thus, greater speeds and therefore greater manufacturing efficiencies can be realized by reducing the mass to be moved. Considerable progress has been made in reducing the mass of the stage or table in machines that fabricate and package integrated circuits or “IC's”. Lightweight materials such as aluminum or composites have replaced traditional but heavy steels and cast irons where possible. Accordingly, in an IC wirebonding machine, for example, the stage supporting the semiconductor “chip” to be wire bonded may have a mass of only a few kilograms. Until now, however, not much effort has been expended in reducing the mass of the rails that make possible the low friction x-y motion of the stage. Thus, the rails may make up a significant fraction of the total mass of the stage.

[0009] Many reinforced metals, or metal matrix composite (“MMC”) materials, possess a number of attractive attributes for a bearing/guideway application, specifically low specific gravity compared to steels, and high elastic modulus. Many of these MMC's are reinforced with ceramic materials, and accordingly are quite wear resistant in dynamic contact with metals. One general problem with using MMC's as bearing materials is the lack of knowledge or experience in engineering or refining the material for this type of application. For example, many of these MMC's, particularly those employing silicon carbide as reinforcement, are simply too abrasive of the steel ball or roller bearing materials in which they are in contact.

[0010] The prior art steel rails against which the hardened steel bearings run have excellent low friction and wear resistance properties. Further, a large experience base exists for steels, including those grades suitable for bearing applications. The problem with steel is its mass; specifically, tool steel may have almost three times the mass of a reinforced aluminum composite component of the same volume. What is needed is a rail that retains the beneficial properties of tool steel, such as low friction and wear resistance, but features the low specific gravity and high modulus of more advanced materials, such as composites.

SUMMARY OF THE INVENTION

[0011] The instant invention substitutes a portion of an existing hardened linear guideway with a material having high elastic modulus but low mass relative to the substituted material. In particular, a “macrocomposite” linear guideway is produced, whereby a hard surface guideway material is maintained as the wear resistant, low friction surface intended to be in contact with one or more bearings, and this surface is backed up or supported by a rigid but lightweight substrate. Viewed in the alternative, the instant macrocomposite guideway comprises a rigid, lightweight substrate clad with a hard surface layer.

[0012] In one preferred configuration, a method is provided for making a rail component of a linear guideway that has at least two rails and a bearing assembly sandwiched between the two rails. The method includes (a) providing a substrate material formed in the shape of the rail and having a surface positioned to face the bearing assembly; (b) permanently depositing a hard wear layer onto the surface through a coating process; and (c) the substrate is made of a material having a density less than that of a material of which the hard wear layer is made.

[0013] In another aspect of the invention, instead of separate, discrete rails for the linear guideway, at least one rail is integrated into some desired machine, specifically into that component of the machine that supports and moves the workpiece.

[0014] One application for the present macrocomposite guideway is for a stage or carriage for wirebonding microprocessor chips. Here, the substrate may be an integral part of the chassis of the stage, or it may be entirely separate, with the resulting macrocomposite guideway subsequently being fastened to the stage.

DEFINITIONS

[0015] “Linear guideway”, as used herein, means an assemblage of rails and bearing element(s) and all parts necessary to accomplish low friction linear motion. (The term “Gib” has been used in a similar manner in certain prior patent documents).

[0016] “Bearing assembly” or “Roller bearing assembly”, as used herein, refers to the collection of bearing elements or bearing bodies and any supporting structure that fits into the bearing race such that the bearing elements or bodies contact the rails.

[0017] “Bearing race”, as used herein, refers to the space defined by the rails into which the bearing assembly is placed.

[0018] “Lightweight body” or “Lightweight material”, as used herein, means a body or material having or engineered to have a density less than that of hardened steel. Thus, “lightweight material” in the context of the instant disclosure not only includes materials having a low theoretical density such as aluminum, silicon, magnesium, beryllium and titanium, but also includes materials specifically processed to meet the above criterion.

[0019] “Rails”, as used herein, refers to the articles or machine elements against which the bearings move.(The term “Linear guideway” has been used in a similar manner in certain prior patent documents).

[0020] “Macrocomposite”, as used herein, means a unitary article made of at least two materials that differ in at least one important property and which are not distributed uniformly or regularly throughout the article. Here, “unitary” means that the materials are joined to one another with the intent that the bond be permanent. Thus, in the context of the instant disclosure, a macrocomposite does not require any constituent material to be a “composite” material according to the common meaning and usage of the term.

BRIEF DESCRIPTION OF THE FIGURES

[0021]FIG. 1 is a cross-sectional schematic view of a macrocomposite linear guideway according to the instant invention such as might be employed in a motion control application such as the movable stage of a semiconductor manufacturing machine;

[0022]FIG. 2 is a cross-sectional schematic view of a prior art linear guideway;

[0023]FIG. 3 is an isometric view of upper and lower stages of a motion control system of a machine showing how the stages move with respect to one another and with respect to the base of the machine to produce low friction motion within a defined region of a plane;

[0024]FIG. 4 is similar to FIG. 1 except that one of the rails of the macrocomposite linear guideway is integrated or built in to the movable chassis or stage of the machine;

[0025]FIG. 5 is a perspective view of a female V-shaped rail substrate prior to receiving a hard wear coating;

[0026]FIG. 6 is a schematic view showing the hard wear coating being applied to the rail of FIG. 5;

[0027]FIG. 7 shows a cross-section of an integrated needle roller bearing system with hard wear coated rails;

[0028]FIG. 7A shows a cross-section of an integrated crossed roller bearing system with hard wear coated rails;

[0029]FIG. 8 is a cross sectional view illustrating an alternative linear guideway geometry for accomplishing low friction linear motion; and

[0030]FIG. 8A is a side view of the alternative linear guideway of FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

[0031] In accordance with the objectives of the instant invention, an existing linear guideway made from an old material well known in the art is replaced in part with a material having high elastic modulus but low mass relative to the substituted material. In particular, a “hybrid” guideway is produced, whereby a “traditional” or hard guideway material is used as the wear resistant, low friction surface intended to be in contact with one or more bearings, and this surface is supported with a stiff yet lightweight substrate material. Thus, the new hybrid guideway comprises a macrocomposite material.

[0032] The hard wear bearing surface may be attached to the lighter weight substrate by various means, including direct thermal spray deposit, electro-plating, adhesive, bonding, mechanical fasteners or other mechanical means such as friction or interference fit. For example, the hard wear surface can be formed by deposition of the hard material such as tungsten carbide onto a substrate of material such as beryllium-aluminum. A preferred method for the deposition is an HVOF thermal spray coating. In this example, a guideway having a hard wear resistant surface for the bearings combined with a lightweight substrate is formed to create a rail much lighter in weight than prior art rails.

[0033] Among the application areas for such a lightweight rail is in the field of semiconductor fabrication equipment, and in the motion control systems, e.g., the “stages” of integrated circuit or semiconductor “chip” wirebonding machines in particular. Referring to FIG. 1, a macrocomposite linear guideway 10 is employed in a motion control application as follows. A one or first rail 12 of the linear guideway 10 is attached to the moving portion 14 of the machine. This portion of the machine is the “stage” or “chassis” or “carriage”, and supports the workpiece to be processed. In FIG. 1, the means of attachment is by mechanical fasteners such as bolt 16. Next, the other or second rail 18 of the guideway 10 is loosely attached to the non-moving portion 20 of the machine opposite the first rail 12. Each rail 12, 18 has a hard wear material layer 22 joined to a land or surface 23 of a substrate 24 of a lighter weight material such as reinforced aluminum composite or beryllium-aluminum alloy, the layer 22 having a hard wear surface 26 for contacting the bearings of the bearing assembly 28 (the surface 26 also referred to as a bearing raceway).

[0034] The stage is then placed onto the machine in the orientation that it will assume during service. The guideway loosely attached to the base of the machine is adjusted to permit the bearing assembly 28 to be inserted into the bearing race 30. The bearing race 30 is the space defined by the hard wear surfaces 26 which are to be in contact with the bearings. After inserting the bearing assembly 28 into the race 30, the loosely attached rail 18 is then adjusted by means of setscrews 32 to take out the slack between the bearings and the hard wear surfaces 26. The setscrews are then further tightened to apply a compressive force against the rails and bearings, thereby “preloading” the bearings. The individual setscrews are then carefully adjusted so that the stage travels smoothly and without play along its intended range of motion. The loosely attached rail is then tightly clamped to the machine body, as for example, by means of bolt 16 a. Other means of attaching linear guideways may be known in the art.

[0035] As an aid in understanding the nature of the invention, reference is made to FIG. 2, which represents the prior art. The difference between FIG. 1 and FIG. 2 is that in FIG. 2, the linear guideway 10 is not a macrocomposite, but instead is fashioned entirely from hardened steel 36, i.e., the rails 12, 18 are made of steel. FIG. 3, also representative of the prior art, shows upper 38 and lower 40 stages of a motion control system in isometric view. FIG. 3 in particular shows how the upper stage 38 attaches to the lower stage 40 through a pair of prior art linear guideways, with each rail 42 a, 42 b, 44 a, 44 b of each linear guideway fastened by bolts 46 to one of the stages (rails 42 a, 42 b forming one linear guideway, rails 44 a, 44 b forming another). The lower stage 40 is similarly attached to the base of the machine (not shown) through a similar pair of prior art rails 48 a, 50 a of other guideways. This Figure also shows how the upper stage 38 is responsible for linear motion in one direction, y, while the lower stage is responsible for motion in a direction orthogonal to that of the upper stage, x. Thus, a workpiece mounted on the upper stage is capable of being positioned at any point within a specific region of the plane defined by directions y and x.

[0036] In another aspect of the instant invention, the macrocomposite linear guideway 10 is not a stand-alone piece, but instead is integrated into the chassis of a movable stage of some machine requiring highly precise motion control, such as a microprocessor wirebonding machine or a coordinate measuring machine, to name two examples. Here, the substrate 24 of the rail 12 and the chassis 14 of the wirebonding stage are made of the same lightweight, stiff material such as metal matrix composite material. Thus, the rail substrate does not have to be independently attached to the chassis, but can be integrated into the chassis design as a unitary piece. For example, the chassis 14 may be cast to a shape that incorporates the guideway substrate shape, or at least a shape having surfaces 23. Lands or surfaces 23 are specifically prepared or machined into the chassis to accommodate the hard wear material 22, which forms the bearing surface 26. The hard wear layer 22 is attached to the land 23 of the chassis by any suitable means, e.g., coating, as further described below.

[0037]FIG. 4 illustrates this aspect of the instant invention in greater detail. Here, the rail 12, opposite the rail 18, is formed as an integral part of stage 14. More specifically, the substrate material 24 backing up and supporting the hard wear layer 22 is part of and the same material as that which forms the chassis of stage 14. The rail 18 remains independent as shown. In one embodiment, an aluminum composite stage chassis 14 is cast and includes surfaces or lands 23 onto which the hardened bearing wear layers 22 are coated. Not only would such a design reduce the mass of the stage by an amount equal to the volume of substrate 24 times the density difference between hardened steel and cast aluminum composite material, but this design further reduces mass by eliminating the need for bolts 16 (see FIG. 1). In the prior art steel rails, the steel bolts may not have added significantly to the total rail mass. With the instant lightweight materials, however, steel bolts represent significant mass-excess mass, in fact, that can be eliminated or significantly reduced with an alternative attachment means.

[0038] To accomplish the purposes of the low mass macrocomposite guideway, in addition to having low mass, the substrate 24 material to which is attached the hard wear layer 22 should possess high stiffness and reasonable strength. Not only must the rails withstand the passive loads and dynamic accelerations during use without fracturing or plastically yielding, but also the rails must not distort or deflect excessively.

[0039] A fairly large number of candidate materials potentially can fulfill these requirements for the substrate 24, including monolithic ceramics, ceramic matrix composites and metal matrix composites. As the primary motivation for building the instant macrocomposite guideway is reducing the mass that must be accelerated/decelerated, as a rough approximation, it is preferable that the “lightweight” substrate material that is to displace some of the steel of the guideway should have a density less than that of steel. More preferred is that the substituted substrate material has a density no greater than about 50 percent that of the displaced steel material.

[0040] Somewhat along these same lines, what is most preferred is that the substrate material have a sufficiently high elastic modulus, such that the volume of substituting material does not have to be greater than what was removed to accomplish the same stiffness. What is preferred is that the specific stiffness (e.g., ratio of elastic modulus to specific gravity) be at least 50 percent higher than that of the material being replaced.

[0041] A significant number of materials fulfill these somewhat more stringent requirements. Certain alloys of light metals meet the requirements. Metal matrix composites, and especially those based upon aluminum or magnesium as the matrix also meet the requirements. Such materials include beryllium-aluminum (Be—Al)(30% to 65% beryllium by weight) and aluminum reinforced with 10 to 30 volume percent silicon carbide particulate (Al—Si—C), both of which are preferred because of their specific stiffness (BeAl being 4 times that of steel, and Al—Si—C being 1.8 times that of steel). Not only do such materials meet the above stiffness and density criteria, but in general, they are also easier to machine than ceramics or ceramic matrix composites. Moreover, these materials can be formed into complex shapes, for example by casting. Accordingly, it is possible to fabricate entire motion control stages or chassis from such substrate materials so that all that is necessary is to clad certain regions with the hardened wear material that is to be the bearing surface.

[0042] Preferred materials for the hard wear layer 22 include hardened steel such as tool steel, various forms of tungsten carbide which include the Stellite materials, alumina-titania, low phosphorous hard nickle, chromium, and other suitable materials. The finished thickness of the hard wear layer 22 should preferably be greater than 10 mils with a thickness of at least 15 mils being more preferred. This is based on the allowable shear stress resulting from the contact stress at the interface of the coating, or insert. 15 mils is believed to be a practical thickness that keeps that shear stress well below the 5 kpsi that most coatings, or attached inserts (e.g., by means of brazing or soldering) can withstand.

[0043] A method contemplated for attaching the hard wear layer 22 for the bearing surface 26 to the lighter weight substrate 22 includes coating the hard material for the layer 22 directly onto the substrate 22.

[0044] During use in most precision equipment, the rail is not expected to experience temperature excursions much beyond ambient temperature, e.g., about 20° C. During fabrication, however, the components to be joined may see temperatures of about 300° C. Large residual stresses could be generated within the bonded bodies should the bodies have large differences in their respective coefficients of thermal expansion (C.E.). Specifically, if a thermal expansion difference between the hard layer and the lightweight substrate exists, then the thermally induced stress will increase in proportion to the degree of the mismatch, the extent of the temperature excursion and the size of the bonding region. These residual stresses could result in the warping of the hybrid rail, particularly as the thickness or cross-section of the rail is reduced, as for example during final machining. A beneficial feature of composite materials is the ability to tailor, at least to a degree, properties such as C.E. In particular, metal matrix composites such as silicon carbide reinforced aluminum can be engineered to have a C.E. close to that of the harder layer, thereby ameliorating this C.E.-induced stress problem. Other composite materials such as reaction bonded silicon carbide systems that feature a co-network of silicon carbide and silicon, and optionally comprising one or more filler materials, also may be C.E.-adjustable, but such materials generally have C.E.'s that are substantially lower than those of steels.

[0045] The closer that the C.E.'s of hard layer 22 and lightweight substrate 24 can be matched, the larger the rail that can be produced for the same degree of C.E. induced stress that is generated. Even though the individual components on an integrated circuit chip are shrinking, the overall size of the silicon wafer from which such IC chips are produced are becoming larger, thus requiring ever-larger stages for the machines that manipulate silicon wafers. With properly matched C.E.'s, it is believed that linear guideways that are an appreciable fraction of one meter, or possible even one meter or more in length can be fabricated using the techniques disclosed in these pages. A lightweight macrocomposite guideway on the order of a meter in length would have a receptive market.

[0046] There are a number of ways in which a low mass, stiff substrate body may be attached to a steel other hard material wear resistant body. In general, and to reduce complexity, permanent attachments such as adhesive or metallurgical bonding are more desirable than nonpermanent attachment scenarios such as mechanical fasteners or mechanical interlocking mechanisms. Still further, because the substrate is expected to carry the bulk of the mechanical load, it is desirable that loads imposed upon the wear surface be transferred effectively to the substrate. Thus, the metallurgical type bonds are preferred over the adhesive bonding arrangements, their higher stiff nesses permitting more effective load transfer. Among the metallurgical bonds, however, welding may not be possible or practical.

[0047] In coating, an engineered layer of material is deposited directly onto the substrate material 24 to form a hard bearing layer 22. Suitable coating processes include HVOF, plasma spray and electro-plating.

[0048] HVOF is a process where liquid fuel and oxygen are fed via a premixing system at high pressure into a combustion chamber to produce a hot, high pressure gas stream which is expanded through a laval nozzle to further increase the gas velocity. The material to be deposited is then injected into the gas stream. The gas stream heats and accelerates the powder particles so that they impact the substrate with extremely high energy.

[0049] Plasma spray is a process where a plasma gun incorporates a cathode (electrode) and an anode (nozzle) separated by a small gap forming a chamber between the two. Direct current is applied to the cathode and arcs across to the anode while at the same time gasses are passed through the chamber. The powerful arc is sufficient to strip the gasses of their electrons to form plasma. As the unstable plasma recombines back to the gaseous state, thermal energy released producing extremely high temperatures. By injecting the coating material into the gas plume, it is melted and propelled toward the substrate material.

[0050] Suitable substrate materials for the coating process include beryllium-aluminum alloy, aluminum-silicon carbide or other suitable light weight base materials such as aluminum. Suitable coating materials should have a modulus of elasticity of at least 25,000,000 p.s.i. Lower modulus materials may be used but could affect bearing life. The wear material should have a Rockwell hardness at least RC 55 or 56 and preferably at least RC 60. The finish for all such surfaces should preferably be at least 8 micro-inches after finish grinding.

[0051] Coating materials for the hard wear bearing surface include hardened steel, tungsten carbide with Cobalt (WC-Co), alumina-titania, Stellite 6, Stellite 60, low phosphorous hard nickle, and chromium. Tungsten carbide coatings on a beryllium aluminum substrate is a presently preferred combination, e.g, tungsten carbide (17% cobalt binder) and tungsten carbide (cobalt and chromium binder).

[0052] The preferred method of coating a chrome hard wear surface onto a beryllium aluminum or aluminum silicon carbide composite is by electroplating.

[0053] Coating Example. Referring to FIG. 5, a female rail 12 is formed from a metal matrix composite substrate 24 having a “V” channel cut into it and measuring about 1 cm in cross-section and about 15 cm long. The rail 12 was cut from wrought 65% Be-35% Al alloy (metal matrix) material. The rail 12 has flat surfaces 23 a, 23 b that will receive the coating to form the hard wear layer 22, and which are prepared by grit blasting to enhance the mechanical adhesion to the coating.

[0054] With reference to FIG. 6, the rail 12 is set up in a fixture 60 for a tungsten carbide (17% cobalt binder) coating of the first surface 23 a. Sheet metal masks 62 are positioned as shown to minimize over spray of the coating. The HVOF nozzle 64 for applying the spray coating is set up at a 95 deg angle from the surface 23 a to be spray coated. The substrate 24 remains at room temperature during the coating process. An air nozzle 66 is set up as shown to cool the layer 22 as it is being applied. This cooling process is believed to minimize shear stresses and warping. For the coating process, the HVOF nozzle 64 traverses along the length of the surface 23 a to apply the coating. A total of approximately 40 passes of spray coating 68 are required to build the coating layer 22 up to the preferred 20-mil thickness which allows for about 5 mils finish grinding as discussed below to retain a thickness of at least 15 mils after grinding. The surface 23 b is then coated in a similar manner.

[0055] The coated rail 12 is then thermal cycled from ambient temperature to 250 deg C several times to eliminate any stresses at the interface of the layer 22 and the substrate 24. The rail 12 was finished machined and the coated layer surfaces 26 (see FIG. 1) ground to a 16 micro-inch finish and a flatness of 40 micro-inches (leaving a coating layer 22 of at least 15 mils thick).

[0056] This entire cycle was repeated to produce a matching male rail 18 a. The set was assembled into a guideway assembly with a complement of 2 mm diameter needle bearings 70 in the bearing race 30 as illustrated in FIG. 7. The assembly was cycled over 100 million times with an oscillating 100 mil move. FIG. 7A illustrates a linear guideway with two female rails 12, 18 (opposing V shaped channels) in configuration for a crossed roller bearing system.

[0057] Use of the present invention should be particularly desirable in certain machines used in semiconductor fabrication, where the lighter the platform or stage holding the semiconductor can be made, the faster the platform can be moved around underneath the work area. One immediate use contemplated is in semiconductor chip wirebonding machines.

[0058] The instant invention is by no means limited to the particular geometry illustrated above. For example, illustrated in FIGS. 8 and 8A is a flat linear guideway 10 geometry (in cross-section and in side view) that may be employed in conjunction with the instant invention for providing high precision, low friction, linear motion. Components labeled with the same number as those above perform a common or similar function. Here, two rails 12 and 18 are, shown, each having a hard wear layer 22 having a bearing surface or raceway 26. Between the two rails is a bearing assembly 28 having a cage 78 holding bearings 80. Here, both rails include the hard wear layer 22 supported by a lighter material substrate 24. The opposing surfaces 26 define the bearing race 30 into which steel bearings 80 are disposed.

[0059] Although the description herein has focused on macrocomposite linear guideways, the concept should extend to other bearing geometries. For example, it should be possible to make a macrocomposite guideway that is circular to accommodate a bearing that runs in a circular track for low friction rotational motion.

[0060] Those of ordinary skill will appreciate that numerous modifications can be made to the invention herein described without departing from the spirit or scope of the invention, as set forth in the claims appended hereto. 

What is claimed is:
 1. A method of making a rail component for a linear guideway that has at least two rails and a bearing assembly sandwiched between said two rails, said method comprising: (a) providing a substrate material formed in the shape of said rail and having a surface positioned to face said bearing assembly; (b) permanently depositing a hard wear layer onto said surface through a coating process; and (c) said substrate being made of a material having a density less than that of a material of which said hard wear layer is made.
 2. A method in accordance with claim 1 wherein said coating process comprises an HVOF process.
 3. A method in accordance with claim 1 wherein said coating process comprises an electroplating process.
 4. A method in accordance with claim 1 wherein said coating process comprises a plasma spray process.
 5. A method in accordance with claim 1 wherein said hard wear material of step (b) comprises steel.
 5. A method in accordance with claim 1 wherein said substrate material comprises a composite material.
 6. A method in accordance with claim 1 wherein said substrate material comprises beryllium.
 7. A method in accordance with claim 1 wherein said substrate material comprises aluminum.
 8. A method in accordance with claim 1 wherein said substrate consists essentially of beryllium and aluminum.
 9. A method in accordance with claim 7 wherein said substrate material further comprises silicon carbide.
 10. A method in accordance with claim 1 wherein said hard wear material of step (b) comprises tungsten carbide.
 11. A method in accordance with claim 1 wherein step (b) comprises depositing said hard wear layer onto said surface until said layer has a thickness greater than 15 mils, and then grinding said layer.
 12. A method in accordance with claim 1 wherein said substrate is made of a material having a specific stiffness at least 1.5 times greater than that of the material of which said hard wear layer is made.
 13. A method in accordance with claim 5 wherein said composite material comprises at least one metal selected from the group consisting of aluminum, beryllium, magnesium and silicon.
 14. A method of making a linear guideway having a bearing race for containing bearings, comprising: (a) providing first and second rails which are combinable to define a bearing race, each of said first and second rails comprising a substrate having a surface; (b) permanently depositing a hard wear layer onto said surface of each of said rails by means of a coating process, said hard wear layer having a wear surface defining at least a portion of said bearing race; and (c) said substrate being made of a material having a density less than that of a material of which said hard wear layer is made.
 15. The method of claim 14 wherein said substrate material has a specific stiffness at least 50 percent greater than that of said material of said hard wear layer.
 16. The method of claim 14 wherein said hard wear layer has a thickness greater than 10 mils, and said substrate material comprises at least one material selected from the group consisting of aluminum, beryllium, magnesium and silicon.
 17. A method of making a stage for use in combination with a linear guideway to provide linear motion of said stage, comprising: (a) providing a chassis having at least one rail attached thereto, said rail comprising a substrate having a surface positioned to face and cooperate with a second rail to define a bearing race between said first and second rails when said first and second rails are combined to form the linear guideway; (b) permanently depositing a hard wear layer onto said surface through a coating process; and (c) said substrate being made of a material having a density less than that of a material of which said hard wear layer is made.
 18. A method in accordance with claim 17 wherein said first rail is integrally formed as part of and of the same material as said chassis.
 19. The method of claim 17 wherein said substrate material has a specific stiffness at least 50 percent greater than that of said material of said layer.
 20. The method of claim 19 wherein said substrate material has a density no greater than about 60 percent of that of said material of said layer.
 21. A linear guideway, comprising: first and second rails, each of said rails having a bearing surface, said first rail having a hard wear layer which includes said bearing surface, and said first rail having a substrate to which said hard wear layer is attached; a bearing between said two rails for roller contact with said bearing surfaces; said substrate being made of a material having a density less than that of a material of which said hard wear layer is made; and said hard wear layer being formed by permanently depositing a hard wear layer onto said substrate through a coating process.
 22. The linear guideway of claim 21 wherein said first rail is integrally formed as part of a stage, and said stage is made of the same material as said substrate.
 23. The linear guideway of claim 21 wherein said substrate material has a specific stiffness at least 1.5 times greater than that of the material of which said hard wear layer is made.
 24. The linear guideway of claim 21 wherein said hard wear layer has a thickness in the range of 10 to 20 mils, and said substrate material comprises at least one material selected from the group consisting of aluminum, beryllium, magnesium and silicon.
 25. A rail for use as in a linear guideway made in accordance with the method of claim
 1. 26. A rail in accordance with claim 25 wherein said hard wear layer has a thickness greater than 15 mils.
 27. A rail in accordance with claim 25 wherein said substrate is made of a material having a specific stiffness at least 1.5 times greater than that of the material of which said hard wear layer is made.
 28. A rail in accordance with claim 25 wherein said composite material comprises at least one metal selected from the group consisting of aluminum, beryllium, magnesium and silicon.
 29. A rail in accordance with claim 25 wherein said coating process comprises one of the following: HVOF, plasma spray, or electro-plating. 